That happens if the drive itself does not report insert/eject events properly.
Some drives are like that. Updating the firmware may work, but some cannot be fixed. (I have one like this, partly for testing this very issue. Pioneer DVD-RW DVR-219L, although the model is only Pioneer branded and not one of the drives they really made themselves. I once found a page detailing the problem, and mentioning this drive in particular, but I can't find it now.)
If you do something in Explorer that forces it to check the status of the drive, it will notice the actual status does not match what the operating system thought it was, and Explorer itself will generate a broadcast event that updates other applications as to the new status. That's why opening an Explorer window causes the drive to appear in Opus. Since this problem used to be quite common, the OS has some mitigations for it, but they cannot fix the underlying issue that the drive itself doesn't tell the computer when a disc is inserted into it.
In fact, Explorer always shows my optical drive under This PC, even though hide empty drives is turned on. I'm not sure if it has recognised it as a problem model or if Explorer simply always shows empty drives in This PC and that option now only affects the folder tree, but it means going to the This PC folder in Explorer probably triggers the drive to be inspected, as it is shown in the list, and that is probably what triggers Explorer to notice the state was wrong and generate the broadcast event with the new state.
If you go to the This PC folder and push F5 in Opus, I think that should make the drive appear. That is what I normally do with my similar optical drive.
Alternatively, you could remove the hideempty
option so the drive is always showing. Or, of course, replace the drive.
The problem could also happen if Opus is running elevated (i.e. the whole dopus.exe was launched elevated, not just individual windows via Admin Mode or normal UAC prompts when doing individual operations). If Opus is elevated but the rest of the desktop is not, then the desktop's notifications about media insertion/removal would be blocked from reaching Opus. But I don't think that is what is happening for you, as it would mean the drive did not appear when you opened the Explorer window. So I suspect it is the drive itself not sending the events, unless something like antivirus is blocking things (always another possibility).